Process in the roasting of ores for removing quantities of tin contained therein

ABSTRACT

There is provided a process for extracting or expelling tin from ores containing said metal by roasting the ore in a fluidized bed furnace and by so correlating the quantity and concentration of the oxygen bearing gas fed to the furnace that the partial pressure of oxygen in the resulting roaster gas lies adjacent but not below a cruve obtained when plotting atmospheres of specific values on log10 PO against temperature in O*C, and so that the said partial pressure of oxygen does not lie above a further curve obtained by plotting other specific values of atmospheres in log10 PO against other specific values of temperature in *C.

United States Patent 11 1 Jensfelt et a1.

[54] PROCESS IN THE ROASTING 0F ORES FOR REMOVING QUANTITIES or TIN CONTAINED THEREIN [75] Inventors: Torsten Eli Jensfelt, Stocksund;

Karl Goran Gb'rling, Lidingo, both of Sweden [73] Assigneez' Boliden Aktiebolag, Stockholm,

Sweden [22] Filed: Aug. 14, I972 21 Appl. No.: 280,222

Related US. Application Data [63] Continuation of Ser. No. 852,610, Aug. 25, 1969,

abandoned.

[30] Foreign Application Priority Data Feb. 4, 1975 3,607,216 9/1971 Van Elst 75/1 FOREIGN PATENTS OR APPLICATIONS 729.177 5/1955 Great Britain 75/85 OTHER PUBLICATIONS Spendlove, M. J. et :11. Experiments on the Recovery of Tin from Low Grade Bolivian Tin Ores by Sulfide Volatilization,-Bureau of Mines Report of Investigations, 5161, U5. Dept. of Interior, September 1955, pp. l-5.

Primary Examiner-Winston A. Douglas Assistant Examiner-O. F. Crutchfield Attorney, Agent, or FirmStevens, Davis, Miller & Mosher [57] ABSTRACT There is provided a process for extracting or expelling Sept. 2, 1968 Sweden 11799/68 tin from ores containing said metal by roasting the ore [52] U S U 75/9 75/26 75/85 in a fluidized bed furnace and by so correlating the 6 quantity and concentration of the oxygen bearing gas 51 Int. Cl C22b I/10 to the i that the P l Pressure of Xygen 58] Field of Search 75/85, 9, 7, 26; 423/96 't mast gas adlacem but below a cruve obtained when plotting atmospheres of spe- [56] References Cited cifiic VZIILIIICS 0;: log z,j P aglainst tempe;ature in 3C, an so t att e 5211 partra pressure 0 oxygen oes UNITED STATES PATENTS not lie above a further curve obtained by plotting Mitchell other specific alues of atmospheres in log P02 against other specific values of temperature in C. 3:386:8l5 6/1968 Gorling et a1 75/9 11 Claims, 2 Drawing Figures to yP p alm "5 HI I N r g 2 03 i II I /0 l/ n F9 4 tempera fare C I PROCESS IN THE ROASTING OF ORES FOR REMOVING QUANTITIES OF TIN CONTAINED THEREIN This is a continuation of application Ser. No. 852,610, filed Aug. 25, 1969, and now abandoned.

The present invention relates to a process for roasting a material for the purpose of extracting from said material the content of tin contained therein. The process is particularly suited for recovering and/or removing tin from sulphidic and oxidic ores which contain small quantities of said metal, although the process can also be applied to recover tin from sulphidic or oxidic ores which are relatively rich in tin. Although a valuable metal in many fields of use, the presence of tin is undesirable in iron goods.

In known processes the tin content is normally leached from the tin ore, although processes in which the tin is volatilized are also known. The former process is often accompanied with great difficulties. It is necessary when practising this former process to work in batches and in certain instances also to supply external heat. Other processes, which includes direct heating by combustion of sulphide or intermixing the fuel and flux, are accompanied with difficulties in controlling the process conditions. Multistage roasting has also been suggested as a process for tin extraction.

For example, it has been suggested that the process is carried out in two fluidized bed furnaces of which one is superposed on the other, the ore being introduced first to the upper reactor, where the tin compounds are volatilized by means of roasting gases obtained from a lower sulphide roasting furnace.

The tin laden gases are passed from the upper reactor to a tin recovery system, while the residue of the partially desulphurized ore with reduced tin content is transferred to the sulphide roasting furnace, where the gases with whose help the tin is volatilized in the upper furnace are formed.

Thus, in the upper bed is effected a partial roasting of sulphide material with a gas containing some oxygen and arriving from the final roasting stage in the lower bed. The atmosphere in the upper bed will contain a relatively high content of elementary sulphur, which coacts to convert the existing tin oxide to tin sulphide, which is much more volatile than the oxide. The present invention, however, affords the possibility of expelling or extracting in a one-stage process a major portion of the tin content together with a major portion of the contents of arsenic, antimony, lead and sulphur, by roasting in accordance with a modification of the known magnetite yielding roasting process described in Swedish Pat. No. 204,002.

It has now been surprisingly discovered that the content of elementary sulphur which can be reached in said roasting process is to a great extent sufficient to form tin sulphide, which can be extracted thereby from the roasted goods. The possibility of expelling tin at a given temperature is dependent on the content of elementary sulphur and S02 in the gas. The quantity of tin which can be expelled stands in relation to the partial pressure of sulphur of the roaster gas and the quantity of the roaster gas formed during the roasting process. The larger the amount of tin to be removed at a given temperature the higher the partial pressure of sulphur and the quantity of roasting gas required.

when roasting sulphur containing iron materials, preferably pyrites and pyrrhotites, the process of the present invention requires that the roasting process be carried out so that the partial pressure of sulphur in the roaster gases is so high that the tin will exist in sulphide form but not so high that FeS can not be roasted off. Under these roasting conditions the iron content in the roasted goods will substantially exist as magnetite. The solid material is removed while maintaining its temperature from the formed roaster gas in a suitable way while the formed and volatilized tin sulphides accompany the roaster gases. Separation of roasted goods accompanying the gas can be effected. for example, in hot cyclones. The gas formed during the roasting process and which contains a high content of S0 may. for example, be used for manufacturing sulphuric acid. To prevent the departure ofthe formed elementary sulphur as waste or to prevent difficulties arising during subsequent gas purification processes the roaster gas is added with a gas containing oxygen after the dust separating stages, the formed elementary sulphur being oxidized to sulphur dioxide, in accordance with Swedish Pats. Nos. 204,002 and 227,188. At the same time the tin sulphide would be oxidized to tin oxide. The tin oxide is separated in enriched form from the roaster gases in electrofilters, sack filters, scrubbers or like devices.

ln order to be able to volatilise the tin present in the ore, the tin possibly existing as tin oxide, it must first be converted to sulphide form, which is more volatile. As mentioned in the aforegoing, this can only be achieved if a certain quantity of sulphur is present in the gas in elementary form during the roasting process. The thermodynamic conditions for the existence of SnS are such that a specific sulphur pressure must prevail in the roaster gas. This pressure is in specific relationship to the pressure of oxygen during'roasting, and hence the process variables in the present process can be expressed as the partial pressure of oxygen in the roaster gas in relation to the temperature.

The pressures of sulphur necessary to effect volatilization of tin vary in dependence of the temperature and the quantity of tin in the material and the quantity of roaster gas.

Experiments have shown that it is possible to expel tin to a large extent if certain conditions are fulfilled with regard to the temperature and air-sulphide relationship. The manner in which the roasting process should be adjusted with regard to said factors is illustrated in the following table.

a total tin pressure on 10' atmospheres can not be reached at 800C.

The table exhibits the values of the partial pressure of sulphur and the therewith correlated partial pressure of oxygen necessary in order that the total tin pressure reaches to 10, 10*, 10' atmospheres respectively at different temperatures. ln FIG. 1 there is shown a graph in which the ordinate is they partial pressure of oxygen plotted as log and the abscisa the temperature plotted in C. The lower limit for the pressure of oxygen is represented by curve ll (the numerical values being found in the table) and the pressure should never being allowed to fall below this limit if a complete sulphide roasting is to be obtained. Curve I shows the highest pressure of oxygen which can be reached in the roaster gas at equilibrium over magnetite. Curve 111 shows the highest pressure of oxygen in the roaster gases corresponding to the lowest pressure of sulphur which must be achieved in order to obtain a total tin pressure in the roaster gases of l atmospheres. In a similar manner, the curves IV and V correspond to the maximum pressure of oxygen for obtaining a total tin pressure of and 10' atmospheres. The partial pressure of oxygen in the roaster gas must be restricted so that it does not exceed the corresponding value of a lowest tin pressure of 10" atmospheres, which is sufficient to remove small quantities of tin corresponding to the smallest tin quantities which can be envisaged during a purification process. Lower pressures of sulphur results in a reaction speed which is too low from a practical point of view. Curve ill therefore represents the upper limit of the partial pressure of oxygen, in accordance with the invention.

When carrying out the tin expulsion process of the invention it is to advantage to work at the highest possible partial pressure of sulphur with regard to the reaction time, i.e. as close to the curve II as is practically possible. This is, of course, of special significance when r the tin content of the material is high.

When practicing the process of the invention, tincontaining ore bearing iron sulphide or mixed with iron sulphide in finely divided form is introduced into a furnace, in which it is suspended in a stream of gas, consisting of an oxygen-containing gas, which is introduced in such quantities and at such concentration that the partial pressure of oxygen in the resulting roaster gas lies adjacent but not below the curve which corresponds to the pertinent values in a diagram where l0g P in atmospheres is plotted as the ordinate against the temperature in C plotted as the abscissa, the curve corresponding to the following numerical values.

and that the partial pressure of oxygen does not exceed the curve defined by the following pertinent values log p p in atm. temp. C

-Continued 03mm,. pin atm. temp. "C

whereafter the roasted goods are separated from the roaster gas at such a temperature that the tin compounds exist in gas form.

The partial pressure of oxygen in the roaster gases must be adjusted within the above area in order that the tin may be expelled during simultaneous complete roasting.

As previously mentioned, the process of the invention is primarily intended for recovering tin from raw materials which contain low contents of this metal, but may also be used to advantage in ores which contain high contents of tin. In this latter instance, the pressure of sulphur is raised, i.e. the relationship of air to sulphide is adjusted so that a lower partial pressure of oxygen is obtained. The values of oxygen pressure which correspond to a total tin pressure of 10' atmospheres have been given in a subordinate claim. If completely oxidic tin raw materials or such materials having a low content of sulphide are to be treated it is convenient to coroast the ore with one of the iron sulphide raw materials, so as to obtain the necessary pressure of sulphur. It is also possible to coroast other iron raw materials, for instance oxidic raw materials, to convert these to magnetite, which may then be transferred if desired while hot, to appropriate further treatment processes; the one determining condition being that it should be possible to maintain the sulphur pressure within the defined area.v

The ore is introduced into the furnace in such a form that fluidizing can be maintained, i.e. corresponding normal grain size of fine pyrite or flotation slag.

The roasting process is suitably carried out in a fluidizing furnace or other type of furnace where granular material is suspended in a gas stream.

FIG. 2 graphically illustrates the various stages in the process of the present invention. A fluidizing furnace l, to which raw material is introduced at 2 and air at 3, is provided with a gas outlet 4 through which the gas is passed to a cyclone 5 where, while maintaining a high temperature, solid material is separated and combined at 6 with any material which has been removed from the bed at 7. The gas is passed from the cyclone 5 to an after-burning chamber 8 where all remaining elementary sulphur is combusted to sulphur dioxide. Air is passed to the after-burning chamber 8 at 9. The gas is then cooled, suitably with water, in a washing tower or indirectly in a waste gas boiler 10, whereafter the cooled gas is passed to an electrofilter 11. The tin compounds are separated as a solid material, either in the washing tower or in the electrofilter, and are removed at 12 or 13 to a plant for optional further purification. The gas containing sulphur dioxide is removed at 13 and used, for example, in the manufacture of sulphuric acid.

The partial pressure of oxygen in the furnace is adjusted by metering ore and air in a predetermined relationship. The quantity of one component is suitably held constant while the other is controlled. The adjustment of the pressure can be controlled in several ways.

A suitable method in this context is to determine con- 5. The process of claim 1, characterized in that subtinuously the content of sulphide and magnetite in the sequent t separating the solid material the roaster outgoing material. gases are supplied with oxygen for co mbusting sulphur The temperature in the furnace can be regulated by 10 Sulphur dioxide- I I adding oxidic material in hot or cold condition or by h Process of claim chafactel'lled f f the steam generating cooling loops direct Spraying of ma ority of the roasted goods are separated within the uid, referabl water, or a combination of these methfurnace and removed i from the i ods. p y 7. The process of claim 1, characterized in that the What is claimed is: major portion of the roasted goods is entrained with the 1. A process for volatilizing the tin content of an ore 10 gas and Separated thatch-Om outslde f 8. The process of clatm 1, characterized in that oxidtc g a i g gg zggfzzig g igi l gjz fit ggfs iron material introduced to the furnace in addition to q g the sulphide and tin-containing material.

bearing iron sulphide 1S continuously introduced into a 9 The process of Claim 1 characterized in that the P bed of Sam m a fu mace wh'ch tin sulphide is removed from the roaster gas by cooling supplied with an oxygen-containing gas in such quantiand washing with waer in a washing towen ties and concehtraflon that the P l Pressure 10. A process for volatilizing the tin content of an ore of Oxygen m the resumhg rcfastehgas hes l'f but in a one-stage process according to the fluidized bed not below the curve which a blhary coordlhate Y technique, characterized in that tin-containing ore Wherein the Partial Prfissure of oxygen in atmobearing iron sulphide mixed with iron sulphide in finely spheres. xpr ssed in t rms of og P0,. as the ordinate, divided form is continuously introduced into a furnace is plotted against the temperature in degrees Centiwhich is supplied with an oxygen'containing gas in such grade, as the abscissa, passes through the following quantities and at such concentration that the partial points: pressure of oxygen in the resulting roaster gas lies adjacent but not below the curve which in a binary coordinate system, wherein the partial pressure of oxygen in m u Temperature C atmospheres, expressed in terms of log P as the ordi- 9 3 1 100 nate is plotted against the temperature in degrees centi- -i0.8 i000 grade, as the abscissa passes through the following -l2.0 900 oin l3.4 800 p ts l5.0 700 gin u Temperature C and that said partial pressure of oxygen does not ex- 33 I100 ceed an analogous curve passing through the following 35 $23 888 points: -l3.4 I 800 l5.0 700 L0 P Temperature ?C I gm and that said partial pressure of oxygen does not ex- 2.91 :688 ceed an analogous curve passing through the following 7:9 900 poms: 9.7 800 -l 1.7 700 Log P,2 Temperature "C 5 4 H00 whereafter the roasted goods are separated from the 6.7 1000 roaster gas at such a temperature that the tin com- 388 pounds exist in gas form. -11'7 700 2. The process for volatilizing the tin content of an ore as described in claim 1, characterized in that a oxygen-containing gas is introduced in such a quantity that resulting partial pressures of oxygen in the roaster gas do not exceed the pressure which is represented in the diagram by the following points.

whereafter roasted goods are separated from the roaster gas at such a temperature that the tin compounds exist in gas form.

11. The process for volatilizing the tin content of an ore as described in claim 10 wherein an oxygencontaining gas is introduced in such quantities that the log P atm. temp. "C resulting partial pressure of oxygen in the roaster gas does not exceed the pressure which is represented in T the diagram by the following points- 7.8 1000 8.9 900 l0.7 800 l 2.7 700. LOgiuPa: Temperature "C 7.8- 1000 3. A process of claim 1, characterized in that the fur- 8.9 900 nace is a fluidizing furnace. 12:; ,88

. 4. The process of claim 1, characterized in that the roasted goods are separated from the roaster gases in a hot cyclone. 

-9.3 1100 -10.8 1000 -12.0 900 -13.4 800 -15.0 700 -5.4 1100 -6.7 1000 -7.9 900 -9.7 800 -11.7 700
 1. A PROCESS FOR VOLATILIZING THE TIN CONTENT OF AN ORE IN A ONE-STAGE PROCESS ACCORDING TO THE FLUIDIZED BED TECHNIQUE, CHARACTERIZED IN THAT TIN-CONTAINING ORE BEARING IRON SULPHIDE IS CONTINUOUSLY INTRODUCED INTO A FLUIDIZED ROASTING BED OF SAID ORE IN A FURNACE WHICH IS SUPPLIED WITH AN OXYGEN-CONTAINING GAS IN SUCH QUANTITIES AND AT SUCH CONCENTRATION THAT THE PARTIAL PRESSURE OF OXYGEN IN THE RESULTING ROASTER GAS LIES ADJACENT BUT NOT BELOW THE CURVE WHICH IN A BINARY COORDINATE SYSTEM, WHEREIN THE PARTIAL PRESSURE OF OXYGEN IN ATMOSPHERES, EXPRESSED IN TERMS OF LOG P0, AS THE ORDINATE, IS PLOTTED AGAINST THE TEMPERATURE IN DEGREES CENTIGRADE, AS THE ABSCISSA, PASSES THROUGH THE FOLLOWING POINTS:
 2. The process for volatilizing the tin content of an ore as described in claim 1, characterized in that a oxygen-containing gas is introduced in such a quantity that resulting partial pressures of oxygen in the roaster gas do not exceed the pressure which is represented in the diagram by the following points.
 3. A process of claim 1, characterized in that the furnace is a fluidizing furnace.
 4. The process of claim 1, characterized in that the roasted goods are separated from the roaster gases in a hot cyclone.
 5. The process of claim 1, characterized in that subsequent to separating the solid material the roaster gases are supplied with oxygen for combusting sulphur to sulphur dioxide.
 6. The process of claim 1, characterized in that the majority of the roasted goods are separated within the furnace and removed direct from the bed.
 7. The process of claim 1, characterized in that the major portion of the roasted goods is entrained with the gas and separated therefrom outside the furnace.
 8. The process of claim 1, characterized in that oxidic iron material is introduced to the furnace in addition to the sulphide and tin-containing material.
 9. The process of claim 1, characterized in that the tin sulphide is removed from the roaster gas by cooling and washing with water in a washing tower.
 10. A process for volatilizing the tin content of an ore in a one-stage process according to the fluidized bed technique, characterized in that tin-containing ore bearing iron sulphide mixed with iron sulphide in finely divided form is continuously introduced into a furnace which is supplied with an oxygen-containing gas in such quantities and at such concentration that the partial pressure of oxygen in the resulting roaster gas lies adjacent but not below the curve which in a binary coordinate system, wherein the partial pressure of oxygen in atmospheres, expressed in terms of log P0 , as the ordinate is plotted against the temperature in degrees centigrade, as the abscissa passes through the following points:
 11. The process for volatilizing the tin content of an ore as described in claim 10 wherein an oxygen-containing gas is introduced in such quantities that the resulting partial pressure of oxygen in the roaster gas does not exceed the pressure which is represented in the diagram by the following points: 